Optimization of semio-chemicals for savannah tsetse control through 'push','pull' and 'push-pull' tactics in Kenya

Abstract

A synthetic repellent for savannah tsetse (2-methoxy-4-methylphenol), which is a synthetic analogue of a mild natural repellent (2-methoxyphenol), found in the body odours of tsetse bovid hosts was recently identified. Preliminary field trials indicated that the repellent could provide substantial protection to cattle. The repellent could also be integrated with other tsetse control tactics in a 'push-pull' strategy that uses repellents to `push' the flies away from their hosts, in conjunction with baited traps/targets, which `pull' and kill them. This study evaluated the efficacy of the 'push-pull' tactic in enhancing tsetse suppression rates and disease levels using on-host repellents to `push' and baited traps to `pull' the flies in Shimba Hills, Kwale District, Kenya. From cross-sectional surveys conducted in the area, livestock farmers considered livestock diseases; trypanosomosis, anaplasmosis, East Coast fever and foot-and-mouth disease to be the major constraints to livestock production in the area. Trypanosomosis was the most important compared to other diseases. Chemotherapy was the most widely used method of controlling the disease. Farmer-based tsetse control strategies were poorly adopted. Most farmers demonstrated awareness about trypanosomosis, its clinical symptoms, aetiology, correct treatment and control measures. Survey of the epidemiology of cattle trypanosomosis in the area indicated that, Glossina austeni, G. brevipalpis and G. pallidipes were found in the area. Trypanosoma congolense and T. vivax were diagnosed in cattle with infection prevalences in the animals varying between 0 and 25%. A field trial conducted in the area to evaluate the effectiveness of 'push-pull' tactic for tsetse and trypanosomosis control indicated that the 'push-pull' might be a more effective way of reducing tsetse populations, trypanosomosis disease incidences and trypanocidal drug use and improving herd health and productivity compared to `push' or `pull'. 'Push-pull' gave significantly higher reduction (62%) in trypanosomosis incidence compared to `push' (59%) and `pull' (53%) (x2 = 65.4; df = 2; p <0.001). Risk of transmission of trypanosomosis in the controls was upto three times significantly (X2 = 43.2; df= 1; p <0.0001) higher than protected cattle. Body weight, body condition and packed cell volume levels were significantly (F = 48.9; df = 1; p <0.01) higher in protected cattle than controls. Percentage reduction in G. pallidipes relative density in 'push-pull' was 83% compared to 77% in `pull' sites. Households with protected cattle recorded significant reduction in trypanocidal drug use (X2 = 11.8; df = 1; p = 0.003). Following the trial, livestock farmers' perceptions on the impacts of the repellent and traps on tsetse challenge and trypanosomosis risk were assessed. Most farmers considered significant reduction in trypanocidal drug use, disease incidence and tsetse population to be the most important benefits of repellents and traps. Additional benefits included quieter grazing, protection of goats and opening up of previously avoided fields for grazing and crop production. Most farmers preferred repellents or traps or both to current methods of tsetse and trypanosomosis control. All farmers preferred repellents to traps. With a view of increasing the potency of the `pull' component, trials conducted to evaluate the attractiveness of aldehyde blends showed that the blends when used alone did not significantly increase trap catches (x2 = 0.61; df = 1; p = 0.461), but when combined with cow urine and/ or acetone, they increased the catches, although this was not statistically significant (x2 = 0.85; df = 1; p = 0.644). Repellents could be integrated with other tsetse control techniques such as traps in enhancing tsetse and disease suppression.